Photochemistry of some square-planar and octahedral platinum complexes

Abstract

The photochemical reactions of cis-Pt(gly)z, PtC12-, and PtBrs2-are investigated and their mechanisms are discussed. By using radioisotopic techniques, it is demonstrated that the cis + trans photoisomerization of Pt(g1y)z takes place by an intramolecular twisting mechanism. An attempt is made to correlate this mechanism with available information on the structure of excited states of square-planar complexes. PtC12-and PtBr62-undergo photoaquation reactions irradiating either in the charge transfer or in the ligand field bands. The quantum yield values of the photoaquation reactions are reported and discussed on the basis of the energy level diagrams of the two complexes. A comparison is also made between photoaquation and photoexchange reactions of PtBre2-, and it is shown that no relation exists between their mechanisms.

Primary reactions in the photochemistry of hexahalide complexes of platinum group metals: A minireview

“…Note that a recent study on the photochemistry of Pt IV Br 6 2À in aqueous solutions [84] supports the hypothesis by Balzani et al [80][81][82] on the multi-stage photoaquation of the complex. The authors re-examined the quantum yields of the first stage, obtaining the value of 0.39 in unbuffered aqueous solutions, 0.29 in pH 6.86 buffer, and 0.6 in 1 M HElO 4 [84].…”

“…Adamson and Sporer [42] found that the quantum yield of the photoinduced ligand exchange in the PtBr 6 2À À ÀBr À system significantly exceeds unity, postulating chain reactions to explain this fact. They assumed that the primary photolysis step was the homolytic cleavage of the PtÀ ÀBr bond with the formation of a According to a different mechanism proposed by Balzani and co-workers [80][81][82], the cleavage of the PtÀ ÀBr bond is heterolytic and the Pt IV Br 5 (H 2 O) À aquated complex is the primary product of the photochemical reaction:…”

Photochemistry of PtBr6 2− in aqueous solution

“…1, curve 1) coincides with that described earlier. 1,7 The intense charge transfer (CT) band with a maximum at 226 nm (ε = 70000 L mol -1 cm -1 ) corresponds to the electron transfer from the t 1u (σ) orbital localized on the ligands to the unoccupied e g (σ*) orbital. Less intense charge transfer bands at 310 and 365 nm (ε = 17 800 and 7400 L mol -1 cm -1 , respectively) correspond to the tran sitions from the t 1u (π) and t 2u (π) orbitals of the bromine atom to the e g (σ*) orbital.…”

Photoactivation of trans diamine platinum complexes in aqueous solution and effect on reactivity towards nucleotides

“…Photolytic reactions of square-planar platinum(II) complexes in aqueous solutions include photoaquation and photoisomerizations [18,20,22]. For example, the photoaquation of cisand trans-[Pt(NH 3 ) 2 Cl 2 ], with the concomitant release of chlorido ligands, has been previously reported and the quantum yield values for the photolysis reaction of both isomers determined [20].…”

“…UVA light promotes the loss of the second chlorido of transplatin and also promotes DNA binding and cytotoxicity [21]. Here we investigate the possibility of using irradiation to activate the cytotoxic Pt IV mixed diamine trans complex trans-[Pt IV Cl 2 (OH) 2 (dimethylamine)(isopropylamine)], 1, and the Pt II analogue, trans-[Pt II Cl 2 (isopropylamine)(methylamine)], 2 ( Figure 1) through photoreduction [22,23] and photosubstitution. We report the effect of irradiation on the aqueous behaviour of complexes 1 and 2.…”